Acetic acid, one of the more important aliphatic intermediates, quantitatively ranks among the commodity chemicals produced in large tonnage quantities. However, availability of acetic acid for downstream applications can be limited at times since availability and price of feedstocks for the production of acetic acid are subject to constant change. For example, availability of hydrocarbon feedstocks such as ethylene, butane and butenes from petroleum sources and natural gas can vary widely depending upon supplies of crude oil upon the world market, capacity of petrochemical producers and demand for products which utilize these same hydrocarbons as feedstocks. An example is polyethylene from ethylene.
Acetic acid can be manufactured by one of several processes, i.e., from acetaldehyde or alkanes and alkenes by oxidation, by carbonylation of methanol, among others. Some of these other processes include the oxidizing of methylcyclohexane to produce acetic acid and formic acid, U.S. Pat. No. 3,247,249; oxidation of ethyl alcohol in the presence of a solid palladium metal containing catalyst, U.S. Pat. No. 3,739,020; oxidation of ethyl alcohol in the presence of at least one ketone such as methylethyl ketone and at least one aldehyde such as acetaldehyde and using air, cobalt acetate catalyst and acetic acid reaction medium, U.S. Pat. No. 3,914,296.
It is well-known that carboxylic acids such as acetic acid can be produced by several liquid phase processes including the liquid phase oxidation of various organic compounds, such as ethanol to acetic acid. For example, in U.S. Pat. No. 2,425,878, a liquid phase oxidation process involves the direct reaction of a lower aliphatic alcohol, ethanol, with oxygen in a liquid phase reaction to prepare acetic acid wherein a rare earth metal catalyst is activated by an aldehyde. Large amounts of catalyst and activator are required.
In the past, high rates of conversion have been obtained in the utilization of ethanol to prepare acetic acid by use of an activator or promoter, as for example, when an aldehyde such as acetaldehyde is used as an activator, as in U.S. Pat. No. 2,578,306.
Although excellent yields of acetic acid are obtained, large amounts of promoter are required, from 1.6 to 9 moles acetaldehyde/mole ethanol oxidized (see U.S. Pat. No. 2,578,306), and from 0.41 to 1.26 moles, acetaldehyde plus methylethyl ketone/mole ethanol, oxidized (see U.S. Pat. No. 3,914,296). The problem with using such large amounts of acetaldehyde and methylethyl ketone to prepare acetic acid from ethanol is, while these compounds oxidize to form acetic acid themselves, these compounds cost more than ethanol or acetic acid and are not commercially available in large enough amounts to make a large scale ethanol to acetic acid process practical. The instant invented process uses a cobalt, manganese, and bromine catalyst system and does not require additional promoters.
Oxidation of ethanol to acetic acid using a cobalt, manganese, bromide catalyst is taught in U.S. Pat. No. 3,247,249, "Preparation of Formic and Acetic Acids by Oxidizing Methylcyclohexane or Paraffin Wax in the Presence of Manganese Bromide." The yield of acetic acid and selectivity to acetic acid are far lower using the reaction conditions described in U.S. Pat. No. 3,247,249 than yields obtained by other processes, including yields obtained by processes using an activator or promoter. Yields of acetic acid given in the examples range from 12 to 19 mole % with formic acid being the major product in 61 to 64 mole % yield.
It has been discovered that utilization of a cobalt-manganese-bromine-containing catalyst without added promoters in a semi-continuous or continuous method makes possible the production of aliphatic carboxylic acids in high conversion, good selectivity and yield from primary aliphatic alcohols. By utilizing different primary aliphatic alcohols as feed, it is possible to obtain the corresponding carboxylic acid, as for example, acetic acid from ethanol, propionic acid from n-propanol, n-butyric acid from n-butanol, etc.
In contrast to the low yields reported in U.S. Pat. No. 3,247,249, under the process conditions of the instant invented process, acetic acid yields of 65 mole % are achieved, and formic acid yield is minimized to as low as 1 mole % with consequent increased yield of acetic acid.
It is therefore an object of the present invention to provide an improved process for the preparation of aliphatic monocarboxylic acids from their corresponding primary alcohol wherein yield of the resulting acid is in good yield in the absence of a promoter or accelerator, although an accelerator can be used.
It is an object of this invention to provide an improved process for the preparation of an aliphatic monocarboxylic acid having from two to six carbon atoms wherein the process is in a liquid phase, semi-continuous or continuous mode, and the catalyst is a cobalt-manganese-bromine catalyst.
It is further an object of this invention to provide an improved process for preparation of acetic acid from ethanol by oxidation in a semi-continuous or continuous mode in the presence of a cobalt-manganese-bromine catalyst wherein reaction progress is controlled as a function of residence time to obtain a good yield of acetic acid and to minimize production of by-products.